Photon sources, which supply single photons at a defined point in time in response to an electrical signal, are needed for spectroscopic applications, and in particular for securely transmitting quantum cryptography keys. Light-emitting diodes (LEDs) are easy to miniaturize, and can be switched very quickly and electrically excited so as to emit very short light pulses. However, the number of photons they emit per unit of time is so large that, while few photons are emitted within the technologically minimally possible pulse duration, this number is still considerably more than one. The more photons are emitted per light pulse, the more limited is the accuracy of spectroscopy or the absolute security of the transmission of keys.
Quantum effects occur in some active solid bodies, as a result of which only one radiative transition at a time takes place at a particular point in time during electrical or optical excitation, during which one photon is released. This means that it is possible to define a time interval during which only a single photon is emitted in each case, and thus the stated requirement is met perfectly. Such a transition can be a recombination of an electron and a hole in a semiconductor, for example, which can only be excited again after a photon has been emitted. These quantum effects, however, require the active solid body to have nanoscale dimensions. The drawback of this is that it becomes very difficult to make electrical contact with such an active solid body for the purpose of excitation. Taking an indirect approach using optical excitation necessitates a separate excitation unit, which converts an electrical signal into light for the excitation. Lucrative mass production of single-photon sources that in each case emit exactly one photon in response to electrical excitation is not conceivable in either of these two ways.
It is thus the object of the invention to make single-photon sources that emit exactly one photon in response to electrical excitation suitable for mass production.
This object is achieved according to the invention by a single-photon source and by a production method. Further advantageous embodiments are disclosed.